In civil excavation projects in urban environments, many restrictions are imposed on operators that substantially increase the operator's capital and operating costs. The operator must generally comply with strict requirements regarding not only the transportation, storage and use of explosives but also airblast, noise, and airborne flyrock particles. "Airblast" refers to pressure waves in air emanating from a rapid release of energy (e.g., a blast). Airblast noise is the audible part of the airblast energy spectrum, having frequencies in the range from 20 to 20,000 Hz. Airblast concussion is the inaudible part of the airblast energy spectrum, having a frequency content below 20 Hz. "Noise" refers to pressure waves in air generated by equipment other than the small charge blasting equipment, such as the drill during formation of one or more holes for small charge blasting and/or the impact breaker during removal of fractured material. "Flyrock" refers to rock particles thrown into the air by the rapid release of energy (e.g., blast). Flyrock may be in the form of a shower of small pieces at relatively high velocities (20 to 50 m/s typical), which typically originate from the collar region of the drill hole. Flyrock may also be in the form of larger pieces of rock at relatively low velocity (1 to 10 m/s typical), which typically originate in the mass of rock excavated from the crater formed by the blasting event.
Existing drill and blast methods may be inapplicable in many applications as a result of these restrictions, even though the blasting methods are the most cost effective method for the specific application. For example, small charge blasting which commonly has a lower seismic and airblast signature, cause less flyrock, and have lower operating costs compared to conventional drill and blast techniques, can nonetheless generate airblast, equipment noise, and/or flyrock levels that exceed the maximum permissible levels in many applications. "Small charge blasting" refers to any excavation method where relatively small amounts of an energetic substance (typically a few kilograms or less) are consumed for each hole in a rock fracturing sequence.